I have called WDW about the fact that my ME booking is not written down anywhere I can print and prove. They told me I just had to find the ME queue and give them my name and ref no. I know my name (!) and have my booking red no. So am trusting that advice. If it doesn't work out I will report back here and pay for a taxi at the airport!!!!!!
just to clear things up. You don't really need a reservation for Disney's Magical Express, you are just supposed to make one.
Disney says you need one, but that's only so that Disney knows, in advance, how many guests will use the service on any given day/time period, in order to manage their routes and buses.
Of course, booking DME is the polite way to do it. But the free shuttle (DME) is a perk of staying onsite.
So, as long as you have a valid hotel booking, DME WILL get you to your resort (always have a printout of your hotel reservation in case their system is down when you get there)
Some guests don't even bother booking it, and even though I think it's rude not to book, they never are refused boarding the DME.
Just go to the ME counter, tell them your name, and you'll soon be on your way to your resort. Don't worry, especially if you have booked DME. If it doesn't show, well, it doesn't show. You still are entitled to a free shuttle to and from your resort.